The church contained a large collection of holy relics and featured, among other things, a 49 foot (15 m) silver iconostasis. It was the seat of the Patriarch of Constantinople and the religious focal point of the Eastern Orthodox Church for nearly one thousand years. It is the church in which Cardinal Humbert in 1054 excommunicated Michael I Cerularius - which is commonly considered the start of the Great Schism.
In 1453, Constantinople was conquered by the Ottoman Turks under Sultan Mehmed II, who subsequently ordered the building converted into a mosque. The bells, altar, iconostasis, and sacrificial vessels were removed and many of the mosaics were plastered over. Islamic features — such as the mihrab, minbar, and four minarets — were added while in the possession of the Ottomans. It remained a mosque until 1931 when it was closed to the public for four years. It was re-opened in 1935 as a museum by the Republic of Turkey.
For almost 500 years the principal mosque of Istanbul, Hagia Sophia served as a model for many other Ottoman mosques, such as the Sultan Ahmed Mosque (Blue Mosque of Istanbul), the Şehzade Mosque, the Süleymaniye Mosque, the Rüstem Pasha Mosque and the Kılıç Ali Paşa Mosque.